316
FXUS63 KBIS 202209
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
509 PM CDT Sat Jul 20 2024

.KEY MESSAGES...

- Isolated to scattered thunderstorms are expected on and off through
  Monday. The threat for severe weather remains low.

- Smoke aloft from distant wildfires will be found through the
  weekend (at least).

- High temperatures will mainly be in the 80s through Monday,
  while some 90s will likely return mid to late week.

&&

.DISCUSSION...
Issued at 143 PM CDT Sat Jul 20 2024

Broad high pressure was in place over the Northern Plains this
afternoon, with a sharp upper ridge extending through the
Canadian Prairies to our northwest, leading to northerly flow
across the forecast area. A few showers and thunderstorms were
ongoing as of 19 UTC across the south central and southeast,
with plenty of instability available but very low shear, so the
expectation is for pulse type, airmass thunderstorms. CAMs have
been relatively inconsistent in timing and location of any
convection, but have been most consistent in the north central
this evening. Overall, we have broad-brushed low POPs across
most of the forecast area through tonight to account for this
potential, especially with limited forcing aloft to increase
chances in any one place. Flow aloft is very weak, so any storms
that develop will be very slow moving.

This northerly flow is also bringing in large amounts of smoke
aloft from wildfires in Alberta and British Columbia. We opted
to not include any near-surface smoke with this update, as
confidence is not quite high enough at the moment, but we cannot
rule out that some locations could experience minor visibility
reductions at some point. Otherwise, the latest HRRR smoke
forecast shows no reprieve from thick smoke aloft, so
continuing the message of hazy skies through the rest of the
weekend.

A similar day is expected on both Sunday and Monday, with highs
in the 80s, light winds, and chances (20-40%) for showers and
thunderstorms. Sunday`s precipitation might be a bit more
spatially limited, while on Monday, a back door cold front and
attendant upper wave (although relatively weak) will bring
higher chances for showers and thunderstorms during the day.
With continued weak shear, the potential for severe
thunderstorms is very low.

As the upper ridge begins to build and shift to east through the
week, temperatures will start climbing, especially across
western North Dakota. The ridge axis is progged to be overhead
of the Northern Plains Wednesday into Friday, with blended
guidance suggesting these will be the hottest days of the
extended period. Highs around 100 degrees F are within reason
mainly on Thursday, with low to medium probabilities of
exceeding this threshold across western North Dakota, especially
in areas along the Montana state border. Lower dew points are
co-located with these hotter temperatures which is keeping
current forecast apparent temperatures just below criteria, but
this will be something to watch in the coming days. Chances for
precipitation are low Tuesday through Thursday.

Upstream of the ridge, a deep upper low is forecast to move
onshore and into the Canadian Prairies late in the week, pushing
the ridge out of the area. More consistent POPs, although low,
begin showing up during this time, while machine learning
probabilities indicate low but increasing chances for severe
thunderstorms late in the week. NBM temperature percentiles
show that after Friday, temperatures will slowly decrease
through the weekend, although expect highs to stay in the mid
80s to mid 90s.

&&

.AVIATION /18Z TAFS THROUGH 18Z SUNDAY/...
Issued at 1243 PM CDT Sat Jul 20 2024

VFR conditions through the TAF period. Isolated to scattered
showers and thunderstorms are possible through most of the TAF
period, but relatively low confidence in timing and location.
For now, only included VCTS this evening at KMOT where there is
higher confidence in storms in the area. Otherwise, light winds
generally from the north to northeast through the period.
Wildfire smoke aloft will be found through the TAF period and
could potentially mix down to the surface and reduce
visibilities, although there is low confidence in this also so
we did not include this at any terminals with this update.

&&

.BIS WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$

DISCUSSION...Jones
AVIATION...Jones